The present embodiments relate to registration of emission tomography and computed tomography. Emission tomography includes positron emission tomography (PET), single photon emission computed tomography (SPECT), or other nuclear imaging. PET uses a detector ring about a patient to detect pairs of gamma rays emitted due to a collusion of a positron with an electron. The positron is generated by a radionuclide (tracer) introduced into the patient. SPECT also uses introduction of a radioisotope (trace). A gamma camera is rotated about the patient to detect gamma rays emitted by the radionuclide. Both PET and SPECT provide functional information, or information about uptake or other physiological function labeled by the tracer.
Computed tomography (CT) measures attenuation of x-rays through the patient from different angles. CT provides anatomical information. The attenuation may be used in reconstruction of the functional information. The effects of attenuation are accounted for in the emission reconstruction. Since the emission and CT information are acquired by different systems, the relative locations of the volumes are registered with each other. The registration between the volumes is determined between an initial emission volume and a reconstructed CT volume. The determined registration is then used through the various iterations of the emission reconstruction to determine the attenuation for each voxel. However, the registration may be sub-optimal due to processing burden and properties of the volumes. The modality (e.g., emission tomography) with the lesser properties (e.g., lower resolution, higher noise, streaks, or other artifacts) may result in less accurate registration.